The present invention relates to circuits for forming matrixes combining three color signals R, G and B into color difference signals - I and Q in accordance with the NTSC color television system. It is also desired to derive a luminance signal Y=k1.multidot.R+k2.multidot.G+k3.multidot.B from the three color signals.
In NTSC color television systems, the color information is transmitted by two color difference signals I and Q while the luminance information is transmitted by way of a luminance signal Y. Matrixes are provided to combine the three color signals R, G and B into the two color difference signals and the luminance signal. The equation for the luminance signal is Y=0.30R+3.59G+0.11B. Starting with this equation, the two color difference signals I and Q have been set as follows: EQU I= 0.74 (R-Y)- 0.27 (B-Y) and EQU Q= 0.48 (R-Y)+ 0.41 (B-Y)
by transformation, the following two color difference equations may be derived: EQU -I= 0.60 R+0.28 G+ 0.32 B and EQU Q= 0.21 R-0.52 G+ 0.31 B
a circuit is shown in the book of P. S. Carnt and G. B. Townsend: "Colour Television", on page 161. This is a circuit for deriving both the color difference signals and the luminance signals from the R, G and B signals. However the circuit requires a great many components. Specifically 9 matrix resistors and 2 inverter stages are required for implementing the coefficients required by the matrix equations. The same number of resistors and inverter stages are required in a circuit shown on page 51 of the book by M. Kaufman and H. Thomas: "Introduction to Color TV". In this book, the luminance signal is derived from the equation Y= 0.30 R+ 0.59 G+0.11 B, while the color difference signals I and Q are derived from the equations EQU I= 0.74 (R-Y)- 0.27 (B-Y) and EQU Q= 0.48 (R-Y)+ 0.41(B-Y).